Field of the Disclosure
The present invention relates to rate adaptation in a wireless environment and in particular to using a semi-open loop technique to achieve an optimized rate.
Description of Related Art
Because the condition of a channel in a wireless environment varies over time, rate adaptation can be advantageously used to achieve optimized throughput in a system with multiple PHY (i.e., physical device) rates. Rate adaptation is especially important in a multiple-input multiple-output (MIMO) system because the number of streams introduces yet another dimension to the channel condition. In general, there are two categories of rate adaptation techniques: a closed-loop rate adaptation and an open-loop rate adaptation.
In the closed-loop rate adaptation, the intended receiver estimates some function of its receive signal (e.g., the channel state information (CSI)), and sends it back to the transmitter. The transmitter determines the optimized rate for its next transmission based on the feedback from the receiver. Unfortunately, this closed-loop rate adaptation has significant system overhead associated with determining the appropriate feedback.
In the open-loop rate adaptation, the transmitter uses trial and error to determine an optimized rate. Thus, the open-loop rate adaptation scheme does not incur any feedback overhead. However, because the transmitter receives no feedback from the receiver, the rate is typically slow to change and can result in errors as incorrect rates are selected.
Therefore, a need arises for a fast and accurate rate adaptation technique that minimizes system overhead.